1. Field of the Invention
The present invention relates to an optical disc drive, and more particularly, to a method of determining bias voltage of a servo signal in an optical disc drive and an apparatus thereof.
2. Description of the Prior Art
An optical disc drive generates servo signals by synthesizing four signals (i.e. A, B, C and D signals) received by an optical sensor. For example, the focus error (FE) signal and the tracking error (TE) signal are two common servo control signals, wherein the FE signal is equal to a signal sum (A+C) minus a signal sum (B+D), and the TE signal is equal to a signal sum (A+D) minus a signal sum (B+D). The optical disc drive controls a pick-up head (PUH) to move in the vertical direction according to the FE signal and controls the pick-up head to move in the horizontal direction according to the TE signal.
Take a focus servo signal as an example. Please refer to FIG. 1 in conjunction with FIG. 2. FIG. 1 is a schematic diagram of the focus servo signal when its focusing position is correct, and FIG. 2 is a schematic diagram of the focus servo signal when a focusing deviation occurs. In FIG. 2, the solid line represents the characteristic in the actual operation, while the dotted line represents the characteristic in the ideal operation. As can be seen in FIG. 2, the focus servo signal is not optimal (unequal to zero) when focusing deviation occurs, and therefore the focus point is not locked to the correct focusing position.